A printed circuit board (“PCB”) is a multi-layer plastic board that includes printed circuits on one or more layers of insulative material. A printed circuit is a pattern of conductors that corresponds to the wiring of an electronic circuit formed on one or more layers of insulative material. The printed circuit board includes electrical traces that are routed on the various layers of the PCB. PCBs also include vias which are solid electrical paths connecting one layer to another layer. A via can be used to connect a trace on one layer of a PCB to another trace on another layer of the PCB. A PCB also includes other layers of metallization for ground planes, power planes or reference voltage planes.
One conventional way to make a PCB is to start with a sheet or strip of dielectric coated with a conductive metal such as copper. Using various drilling, plating, lithographic and metal etching steps a pattern is then formed leaving metal where traces are desired. The traces are on top of the sheet or strip of dielectric. One sheet forms one layer of the PCB.
Another conventional way to make a PCB is to start with a sheet or strip of non-conductive plastic or ceramic, deposit ink in a pattern that forms the conductive traces, sinter the ink to form metal traces. The sheet or strip of non-conductive plastic or ceramic is sometimes referred to as a manufacturing panel. Fiducial markings or coupons are placed on the manufacturing panels. A PCB can have several layers of traces. Five or six layers is common for a multi-layer PCB. Each layer is formed on a manufacturing panel and then the various layers are registered with the fiducial markings or coupons and bonded together. The manufacturing panels form a laminate that includes a number of individual PCBs. The laminate formed is then further processed. Vias or paths from one layer to another layer within the PCB are formed by drilling through the PCB to hit various pads on each of the layers. The pads are generally large enough to account for any inaccuracies associated with routing design or misregistration between the layers of the PCB. A PCB may also include various planes for power, ground reference or another voltage reference. As a result, each PCB requires substantial routing of signal lines and power-supply capability. Design changes are difficult to make. Accounting for inaccuracies, such as making large inner pads for a via, limits the density of the signal carrying lines and makes routing more difficult. Furthermore, the resulting PCB typically has stub traces that may result in undesirable electrical qualities. For example, such stubs vary the impedence and may result in crosstalk between signal lines. Another aspect of current PCBs is that each plate carries a single layer of traces. Once the further processing of laminate formed is complete, the manufacturing panel is cut or singulated to form individual printed circuit boards.
The description set out herein illustrates the various embodiments of the invention and such description is not intended to be construed as limiting in any manner.